diff --git a/app/client/modules/backups/components/create-schedule-form/advanced-section.tsx b/app/client/modules/backups/components/create-schedule-form/advanced-section.tsx
index d7b03e1f..72d3f831 100644
--- a/app/client/modules/backups/components/create-schedule-form/advanced-section.tsx
+++ b/app/client/modules/backups/components/create-schedule-form/advanced-section.tsx
@@ -24,8 +24,8 @@ export const AdvancedSection = ({ form }: AdvancedSectionProps) => {
 					</FormControl>
 					<FormDescription>
 						Advanced: enter one restic flag per line (e.g.{" "}
-						<code className="bg-muted px-1 rounded">--iexclude-larger-than 500M</code>). These are appended to the
-						backup command as-is.
+						<code className="bg-muted px-1 rounded">--exclude-larger-than 500M</code>). Only the supported flag list is
+						accepted.
 					</FormDescription>
 					<FormMessage />
 				</FormItem>
diff --git a/app/server/modules/auth/__tests__/auth.account-and-membership.test.ts b/app/server/modules/auth/__tests__/auth.account-and-membership.test.ts
new file mode 100644
index 00000000..f620fd68
--- /dev/null
+++ b/app/server/modules/auth/__tests__/auth.account-and-membership.test.ts
@@ -0,0 +1,275 @@
+import { beforeEach, describe, expect, test } from "bun:test";
+import { db } from "~/server/db/db";
+import { account, member, organization, sessionsTable, usersTable } from "~/server/db/schema";
+import { authService } from "../auth.service";
+
+function randomId() {
+	return Bun.randomUUIDv7();
+}
+
+function randomSlug(prefix: string) {
+	return `${prefix}-${Math.random().toString(36).slice(2, 8)}`;
+}
+
+async function createUser(email: string) {
+	const id = randomId();
+
+	await db.insert(usersTable).values({
+		id,
+		email,
+		name: email.split("@")[0],
+		username: randomSlug("user"),
+	});
+
+	return id;
+}
+
+async function createOrganization(name: string) {
+	const id = randomId();
+
+	await db.insert(organization).values({
+		id,
+		name,
+		slug: randomSlug("org"),
+		createdAt: new Date(),
+	});
+
+	return id;
+}
+
+async function createMembership({
+	userId,
+	organizationId,
+	role,
+}: {
+	userId: string;
+	organizationId: string;
+	role: "owner" | "admin" | "member";
+}) {
+	const id = randomId();
+	await db.insert(member).values({ id, userId, organizationId, role, createdAt: new Date() });
+	return id;
+}
+
+async function createSession({
+	userId,
+	activeOrganizationId,
+}: {
+	userId: string;
+	activeOrganizationId: string | null;
+}) {
+	await db.insert(sessionsTable).values({
+		id: randomId(),
+		userId,
+		token: randomSlug("token"),
+		expiresAt: new Date(Date.now() + 60_000),
+		activeOrganizationId,
+	});
+}
+
+async function createAccount({ userId, providerId }: { userId: string; providerId: string }) {
+	const id = randomId();
+
+	await db.insert(account).values({
+		id,
+		accountId: randomSlug("account"),
+		providerId,
+		userId,
+		password: providerId === "credential" ? "password-hash" : null,
+	});
+
+	return id;
+}
+
+describe("authService account and membership management", () => {
+	beforeEach(async () => {
+		await db.delete(account);
+		await db.delete(member);
+		await db.delete(sessionsTable);
+		await db.delete(organization);
+		await db.delete(usersTable);
+	});
+
+	test("deleteUserAccount removes the selected account and keeps existing sessions", async () => {
+		const userId = await createUser(`${randomSlug("user")}@example.com`);
+		const credentialAccountId = await createAccount({
+			userId,
+			providerId: "credential",
+		});
+		await createAccount({ userId, providerId: "oidc-acme" });
+		await createSession({ userId, activeOrganizationId: null });
+
+		const result = await authService.deleteUserAccount(userId, credentialAccountId);
+
+		expect(result).toEqual({ lastAccount: false, notFound: false });
+
+		const deletedAccount = await db.query.account.findFirst({
+			where: { id: credentialAccountId },
+			columns: { id: true },
+		});
+		const remainingSessions = await db.query.sessionsTable.findMany({
+			where: { userId },
+			columns: { id: true },
+		});
+
+		expect(deletedAccount).toBeUndefined();
+		expect(remainingSessions).toHaveLength(1);
+	});
+
+	test("deleteUserAccount returns notFound when the account does not belong to the user", async () => {
+		const userId = await createUser(`${randomSlug("user")}@example.com`);
+		await createAccount({ userId, providerId: "credential" });
+		await createAccount({ userId, providerId: "oidc-acme" });
+
+		const result = await authService.deleteUserAccount(userId, randomId());
+
+		expect(result).toEqual({ lastAccount: false, notFound: true });
+	});
+
+	test("deleteUserAccount refuses to delete when it is the user's last account", async () => {
+		const userId = await createUser(`${randomSlug("user")}@example.com`);
+		const onlyAccountId = await createAccount({
+			userId,
+			providerId: "credential",
+		});
+
+		const result = await authService.deleteUserAccount(userId, onlyAccountId);
+
+		expect(result).toEqual({ lastAccount: true, notFound: false });
+
+		const existingAccount = await db.query.account.findFirst({
+			where: { id: onlyAccountId },
+			columns: { id: true },
+		});
+
+		expect(existingAccount).toEqual({ id: onlyAccountId });
+	});
+
+	test("removeOrgMember rehomes active sessions to another organization membership", async () => {
+		const userId = await createUser(`${randomSlug("user")}@example.com`);
+		const removedOrgId = await createOrganization("Removed Org");
+		const fallbackOrgId = await createOrganization("Fallback Org");
+		const membershipId = await createMembership({
+			userId,
+			organizationId: removedOrgId,
+			role: "member",
+		});
+		await createMembership({
+			userId,
+			organizationId: fallbackOrgId,
+			role: "member",
+		});
+		await createSession({ userId, activeOrganizationId: removedOrgId });
+
+		const result = await authService.removeOrgMember(membershipId, removedOrgId);
+
+		expect(result).toEqual({ found: true, isOwner: false });
+
+		const session = await db.query.sessionsTable.findFirst({
+			where: { userId },
+			columns: { activeOrganizationId: true },
+		});
+		const removedMembership = await db.query.member.findFirst({
+			where: { id: membershipId },
+			columns: { id: true },
+		});
+
+		expect(session?.activeOrganizationId).toBe(fallbackOrgId);
+		expect(removedMembership).toBeUndefined();
+	});
+
+	test("removeOrgMember revokes sessions when the removed user has no fallback organization", async () => {
+		const userId = await createUser(`${randomSlug("user")}@example.com`);
+		const removedOrgId = await createOrganization("Removed Org");
+		const membershipId = await createMembership({
+			userId,
+			organizationId: removedOrgId,
+			role: "member",
+		});
+		await createSession({ userId, activeOrganizationId: removedOrgId });
+
+		const result = await authService.removeOrgMember(membershipId, removedOrgId);
+
+		expect(result).toEqual({ found: true, isOwner: false });
+
+		const remainingSessions = await db.query.sessionsTable.findMany({
+			where: { userId },
+			columns: { id: true },
+		});
+		const removedMembership = await db.query.member.findFirst({
+			where: { id: membershipId },
+			columns: { id: true },
+		});
+
+		expect(remainingSessions).toHaveLength(0);
+		expect(removedMembership).toBeUndefined();
+	});
+
+	test("removeOrgMember returns isOwner=true and does not remove owner membership", async () => {
+		const userId = await createUser(`${randomSlug("user")}@example.com`);
+		const orgId = await createOrganization("Owner Org");
+		const membershipId = await createMembership({
+			userId,
+			organizationId: orgId,
+			role: "owner",
+		});
+
+		const result = await authService.removeOrgMember(membershipId, orgId);
+
+		expect(result).toEqual({ found: true, isOwner: true });
+
+		const existingMembership = await db.query.member.findFirst({
+			where: { id: membershipId },
+			columns: { id: true, role: true },
+		});
+
+		expect(existingMembership).toEqual({ id: membershipId, role: "owner" });
+	});
+
+	test("removeOrgMember returns found=false for missing membership and leaves members/sessions unchanged", async () => {
+		const userId = await createUser(`${randomSlug("user")}@example.com`);
+		const orgId = await createOrganization("Existing Org");
+		const otherOrgId = await createOrganization("Other Org");
+		const membershipId = await createMembership({
+			userId,
+			organizationId: orgId,
+			role: "member",
+		});
+		await createMembership({
+			userId,
+			organizationId: otherOrgId,
+			role: "member",
+		});
+		await createSession({ userId, activeOrganizationId: orgId });
+
+		const membersBefore = await db.query.member.findMany({
+			where: { userId },
+			columns: { id: true },
+		});
+		const sessionsBefore = await db.query.sessionsTable.findMany({
+			where: { userId },
+			columns: { id: true, activeOrganizationId: true },
+		});
+
+		const result = await authService.removeOrgMember(randomId(), orgId);
+
+		expect(result).toEqual({ found: false, isOwner: false });
+
+		const membersAfter = await db.query.member.findMany({
+			where: { userId },
+			columns: { id: true },
+		});
+		const sessionsAfter = await db.query.sessionsTable.findMany({
+			where: { userId },
+			columns: { id: true, activeOrganizationId: true },
+		});
+		const membershipStillExists = await db.query.member.findFirst({
+			where: { id: membershipId },
+			columns: { id: true },
+		});
+
+		expect(membersAfter).toEqual(membersBefore);
+		expect(sessionsAfter).toEqual(sessionsBefore);
+		expect(membershipStillExists).toEqual({ id: membershipId });
+	});
+});
diff --git a/app/server/modules/auth/__tests__/auth.controller.security.test.ts b/app/server/modules/auth/__tests__/auth.controller.security.test.ts
index 37dc941b..a4482d01 100644
--- a/app/server/modules/auth/__tests__/auth.controller.security.test.ts
+++ b/app/server/modules/auth/__tests__/auth.controller.security.test.ts
@@ -152,6 +152,42 @@ describe("auth controller security", () => {
 				expect(res.status).not.toBe(401);
 			});
 		}
+
+		test("global admins can delete an account for a user outside their active organization", async () => {
+			const { headers } = await createTestSessionWithGlobalAdmin();
+			const target = await createTestSession();
+
+			const retainedAccountId = Bun.randomUUIDv7();
+			await db.insert(account).values({
+				id: retainedAccountId,
+				accountId: `credential-${retainedAccountId}`,
+				providerId: "credential",
+				userId: target.user.id,
+				password: "password-hash",
+			});
+
+			const removableAccountId = Bun.randomUUIDv7();
+			await db.insert(account).values({
+				id: removableAccountId,
+				accountId: `oidc-${removableAccountId}`,
+				providerId: "oidc-acme",
+				userId: target.user.id,
+			});
+
+			const res = await app.request(`/api/v1/auth/admin-users/${target.user.id}/accounts/${removableAccountId}`, {
+				method: "DELETE",
+				headers,
+			});
+
+			expect(res.status).toBe(200);
+
+			const deletedAccount = await db.query.account.findFirst({
+				where: { id: removableAccountId },
+				columns: { id: true },
+			});
+
+			expect(deletedAccount).toBeUndefined();
+		});
 	});
 
 	describe("invalid session handling", () => {
diff --git a/app/server/modules/auth/auth.controller.ts b/app/server/modules/auth/auth.controller.ts
index b32d583f..21efd34f 100644
--- a/app/server/modules/auth/auth.controller.ts
+++ b/app/server/modules/auth/auth.controller.ts
@@ -49,18 +49,16 @@ export const authController = new Hono()
 	.delete("/admin-users/:userId/accounts/:accountId", requireAuth, requireAdmin, deleteUserAccountDto, async (c) => {
 		const userId = c.req.param("userId");
 		const accountId = c.req.param("accountId");
-		const organizationId = c.get("organizationId");
-
-		const result = await authService.deleteUserAccount(userId, accountId, organizationId);
-
-		if (result.forbidden) {
-			return c.json({ message: "User is not a member of this organization" }, 403);
-		}
+		const result = await authService.deleteUserAccount(userId, accountId);
 
 		if (result.lastAccount) {
 			return c.json({ message: "Cannot delete the last account of a user" }, 409);
 		}
 
+		if (result.notFound) {
+			return c.json({ message: "Account not found" }, 404);
+		}
+
 		return c.json({ success: true });
 	})
 	.get("/deletion-impact/:userId", requireAuth, requireAdmin, getUserDeletionImpactDto, async (c) => {
diff --git a/app/server/modules/auth/auth.dto.ts b/app/server/modules/auth/auth.dto.ts
index 03859b56..eee61222 100644
--- a/app/server/modules/auth/auth.dto.ts
+++ b/app/server/modules/auth/auth.dto.ts
@@ -94,8 +94,8 @@ export const deleteUserAccountDto = describeRoute({
 		200: {
 			description: "Account deleted successfully",
 		},
-		403: {
-			description: "Forbidden",
+		404: {
+			description: "Account not found",
 		},
 		409: {
 			description: "Cannot delete the last account",
diff --git a/app/server/modules/auth/auth.service.ts b/app/server/modules/auth/auth.service.ts
index b350ea02..59b7629c 100644
--- a/app/server/modules/auth/auth.service.ts
+++ b/app/server/modules/auth/auth.service.ts
@@ -97,7 +97,10 @@ export class AuthService {
 
 			if (affectedUserIds.length > 0) {
 				const memberships = await tx
-					.select({ userId: member.userId, organizationId: member.organizationId })
+					.select({
+						userId: member.userId,
+						organizationId: member.organizationId,
+					})
 					.from(member)
 					.where(inArray(member.userId, affectedUserIds));
 
@@ -127,16 +130,6 @@ export class AuthService {
 		});
 	}
 
-	/**
-	 * Check if a user is a member of an organization
-	 */
-	async getUserMembership(userId: string, organizationId: string) {
-		return db.query.member.findFirst({
-			where: { AND: [{ userId }, { organizationId }] },
-			columns: { id: true },
-		});
-	}
-
 	/**
 	 * Fetch accounts for a list of users, keyed by userId
 	 */
@@ -153,7 +146,10 @@ export class AuthService {
 			if (!grouped[row.userId]) {
 				grouped[row.userId] = [];
 			}
-			grouped[row.userId].push({ id: row.id, providerId: row.providerId });
+			grouped[row.userId].push({
+				id: row.id,
+				providerId: row.providerId,
+			});
 		}
 		return grouped;
 	}
@@ -220,7 +216,30 @@ export class AuthService {
 			return { found: true, isOwner: true } as const;
 		}
 
-		await db.delete(member).where(eq(member.id, memberId));
+		await db.transaction(async (tx) => {
+			const fallbackMembership = await tx.query.member.findFirst({
+				where: {
+					AND: [{ userId: targetMember.userId }, { organizationId: { ne: organizationId } }],
+				},
+				columns: { organizationId: true },
+			});
+
+			await tx.delete(member).where(eq(member.id, memberId));
+
+			if (fallbackMembership?.organizationId) {
+				await tx
+					.update(sessionsTable)
+					.set({
+						activeOrganizationId: fallbackMembership.organizationId,
+					})
+					.where(
+						and(eq(sessionsTable.userId, targetMember.userId), eq(sessionsTable.activeOrganizationId, organizationId)),
+					);
+				return;
+			}
+
+			await tx.delete(sessionsTable).where(eq(sessionsTable.userId, targetMember.userId));
+		});
 
 		return { found: true, isOwner: false } as const;
 	}
@@ -241,24 +260,32 @@ export class AuthService {
 	/**
 	 * Delete a single account for a user, refusing if it is the last one
 	 */
-	async deleteUserAccount(userId: string, accountId: string, organizationId: string) {
-		const membership = await this.getUserMembership(userId, organizationId);
-		if (!membership) {
-			return { lastAccount: false, forbidden: true };
-		}
-
+	async deleteUserAccount(userId: string, accountId: string) {
 		return db.transaction(async (tx) => {
+			const [targetAccount] = await tx
+				.select({ id: account.id })
+				.from(account)
+				.where(and(eq(account.id, accountId), eq(account.userId, userId)))
+				.limit(1);
+
+			if (!targetAccount) {
+				return { lastAccount: false, notFound: true };
+			}
+
 			const userAccounts = await tx.query.account.findMany({
 				where: { userId },
 				columns: { id: true },
 			});
 
 			if (userAccounts.length <= 1) {
-				return { lastAccount: true, forbidden: false };
+				return { lastAccount: true, notFound: false };
 			}
 
 			await tx.delete(account).where(and(eq(account.id, accountId), eq(account.userId, userId)));
-			return { lastAccount: false, forbidden: false };
+			// Sessions cannot be tied to a specific account/provider with the current schema,
+			// so keep active sessions intact when unlinking a single account.
+
+			return { lastAccount: false, notFound: false };
 		});
 	}
 }
diff --git a/app/server/modules/sso/__tests__/sso.registration.test.ts b/app/server/modules/sso/__tests__/sso.registration.test.ts
new file mode 100644
index 00000000..8dab023f
--- /dev/null
+++ b/app/server/modules/sso/__tests__/sso.registration.test.ts
@@ -0,0 +1,106 @@
+import { beforeEach, describe, expect, test } from "bun:test";
+import { createApp } from "~/server/app";
+import { config } from "~/server/core/config";
+import { db } from "~/server/db/db";
+import { account, invitation, member, organization, ssoProvider, usersTable, verification } from "~/server/db/schema";
+import { createTestSession, createTestSessionWithOrgAdmin } from "~/test/helpers/auth";
+
+const app = createApp();
+const ssoRegisterUrl = new URL("/api/auth/sso/register", config.baseUrl).toString();
+
+function buildRegisterBody(organizationId: string, suffix: string) {
+	return {
+		providerId: `oidc-${suffix}-${Bun.randomUUIDv7()}`,
+		issuer: "https://issuer.example.com",
+		domain: "example.com",
+		organizationId,
+		oidcConfig: {
+			clientId: "client-id",
+			clientSecret: "client-secret",
+			skipDiscovery: true,
+			discoveryEndpoint: "https://issuer.example.com/.well-known/openid-configuration",
+			authorizationEndpoint: "https://issuer.example.com/oauth2/authorize",
+			tokenEndpoint: "https://issuer.example.com/oauth2/token",
+			jwksEndpoint: "https://issuer.example.com/.well-known/jwks.json",
+		},
+	};
+}
+
+describe("SSO provider registration authorization", () => {
+	beforeEach(async () => {
+		await db.delete(member);
+		await db.delete(account);
+		await db.delete(invitation);
+		await db.delete(ssoProvider);
+		await db.delete(verification);
+		await db.delete(organization);
+		await db.delete(usersTable);
+	});
+
+	test("allows organization owners to register providers for their active organization", async () => {
+		const { headers, organizationId } = await createTestSession();
+
+		const response = await app.request(ssoRegisterUrl, {
+			method: "POST",
+			headers: {
+				...headers,
+				"Content-Type": "application/json",
+			},
+			body: JSON.stringify(buildRegisterBody(organizationId, "owner")),
+		});
+
+		expect(response.status).toBe(200);
+	});
+
+	test("rejects org admins for registration when they are not owners", async () => {
+		const { headers, organizationId } = await createTestSessionWithOrgAdmin();
+
+		const response = await app.request(ssoRegisterUrl, {
+			method: "POST",
+			headers: {
+				...headers,
+				"Content-Type": "application/json",
+			},
+			body: JSON.stringify(buildRegisterBody(organizationId, "admin")),
+		});
+
+		expect(response.status).toBe(403);
+
+		const body = await response.json();
+		expect(body.message).toBe("Only organization owners can register SSO providers");
+	});
+
+	test("rejects users who are owners elsewhere but only members of the target organization", async () => {
+		const { headers, user } = await createTestSession();
+		const targetOrgId = Bun.randomUUIDv7();
+
+		await db.insert(organization).values({
+			id: targetOrgId,
+			name: "Target Org",
+			slug: `target-org-${Date.now()}`,
+			createdAt: new Date(),
+		});
+
+		await db.insert(member).values({
+			id: Bun.randomUUIDv7(),
+			userId: user.id,
+			organizationId: targetOrgId,
+			role: "member",
+			createdAt: new Date(),
+		});
+
+		const response = await app.request(ssoRegisterUrl, {
+			method: "POST",
+			headers: {
+				...headers,
+				"Content-Type": "application/json",
+			},
+			body: JSON.stringify(buildRegisterBody(targetOrgId, "cross-org")),
+		});
+
+		expect(response.status).toBe(403);
+
+		const body = await response.json();
+		expect(body.message).toBe("Only organization owners can register SSO providers");
+	});
+});
diff --git a/app/server/modules/sso/__tests__/sso.service.test.ts b/app/server/modules/sso/__tests__/sso.service.test.ts
index 7c9eef54..dd3ae8c4 100644
--- a/app/server/modules/sso/__tests__/sso.service.test.ts
+++ b/app/server/modules/sso/__tests__/sso.service.test.ts
@@ -1,6 +1,6 @@
 import { beforeEach, describe, expect, test } from "bun:test";
 import { db } from "~/server/db/db";
-import { account, invitation, member, organization, ssoProvider, usersTable } from "~/server/db/schema";
+import { account, invitation, member, organization, sessionsTable, ssoProvider, usersTable } from "~/server/db/schema";
 import { ssoService } from "../sso.service";
 
 function randomId() {
@@ -37,10 +37,20 @@ async function createOrganization(name: string) {
 	return id;
 }
 
+async function createSession(userId: string) {
+	await db.insert(sessionsTable).values({
+		id: randomId(),
+		userId,
+		token: randomSlug("token"),
+		expiresAt: new Date(Date.now() + 60_000),
+	});
+}
+
 describe("ssoService.deleteSsoProvider", () => {
 	beforeEach(async () => {
 		await db.delete(member);
 		await db.delete(account);
+		await db.delete(sessionsTable);
 		await db.delete(invitation);
 		await db.delete(ssoProvider);
 		await db.delete(organization);
@@ -119,6 +129,8 @@ describe("ssoService.deleteSsoProvider", () => {
 				userId: accountUserB,
 			},
 		]);
+		await createSession(accountUserA);
+		await createSession(accountUserB);
 
 		const deleted = await ssoService.deleteSsoProvider(providerId, org);
 
@@ -132,9 +144,14 @@ describe("ssoService.deleteSsoProvider", () => {
 			where: { providerId },
 			columns: { id: true },
 		});
+		const remainingSessions = await db.query.sessionsTable.findMany({
+			where: { userId: { in: [accountUserA, accountUserB] } },
+			columns: { id: true },
+		});
 
 		expect(remainingProvider).toBeUndefined();
 		expect(remainingAccounts).toHaveLength(0);
+		expect(remainingSessions).toHaveLength(0);
 	});
 
 	test("deleting a reserved provider id never deletes credential accounts", async () => {
diff --git a/app/server/modules/sso/middlewares/authorize-registration.ts b/app/server/modules/sso/middlewares/authorize-registration.ts
new file mode 100644
index 00000000..951acfbe
--- /dev/null
+++ b/app/server/modules/sso/middlewares/authorize-registration.ts
@@ -0,0 +1,45 @@
+import { APIError } from "better-auth/api";
+import type { AuthMiddlewareContext } from "~/server/lib/auth";
+import { db } from "~/server/db/db";
+
+export const authorizeSsoRegistration = async (ctx: AuthMiddlewareContext) => {
+	if (ctx.path !== "/sso/register") {
+		return;
+	}
+
+	const sessionToken = await ctx.getSignedCookie(ctx.context.authCookies.sessionToken.name, ctx.context.secret);
+	if (!sessionToken) {
+		throw new APIError("UNAUTHORIZED");
+	}
+
+	const session = await ctx.context.internalAdapter.findSession(sessionToken);
+	if (!session || session.session.expiresAt < new Date()) {
+		throw new APIError("UNAUTHORIZED");
+	}
+
+	ctx.context.session = session;
+
+	if (!ctx.body || typeof ctx.body !== "object") {
+		throw new APIError("BAD_REQUEST", { message: "Missing SSO registration payload" });
+	}
+
+	const organizationId = (ctx.body as Record<string, unknown>).organizationId;
+	if (typeof organizationId !== "string" || organizationId.length === 0) {
+		throw new APIError("BAD_REQUEST", { message: "organizationId is required to register an SSO provider" });
+	}
+
+	const membership = await db.query.member.findFirst({
+		where: {
+			AND: [{ userId: session.user.id }, { organizationId }],
+		},
+		columns: { role: true },
+	});
+
+	if (!membership) {
+		throw new APIError("FORBIDDEN", { message: "You are not a member of this organization" });
+	}
+
+	if (membership.role !== "owner") {
+		throw new APIError("FORBIDDEN", { message: "Only organization owners can register SSO providers" });
+	}
+};
diff --git a/app/server/modules/sso/sso.integration.ts b/app/server/modules/sso/sso.integration.ts
index 01932147..fedfc98e 100644
--- a/app/server/modules/sso/sso.integration.ts
+++ b/app/server/modules/sso/sso.integration.ts
@@ -8,6 +8,7 @@ import { authService } from "../auth/auth.service";
 import { ssoService } from "./sso.service";
 import { validateSsoProviderId } from "./middlewares/validate-provider-id";
 import { validateSsoCallbackUrls } from "./middlewares/validate-callback-urls";
+import { authorizeSsoRegistration } from "./middlewares/authorize-registration";
 import { requireSsoInvitation } from "./middlewares/require-invitation";
 import { resolveTrustedProvidersForRequest } from "./middlewares/trust-provider-for-linking";
 import { isSsoCallbackRequest, extractProviderIdFromContext, normalizeEmail } from "./utils/sso-context";
@@ -143,7 +144,7 @@ export const ssoIntegration = {
 		},
 	}),
 
-	beforeMiddlewares: [validateSsoProviderId, validateSsoCallbackUrls] as const,
+	beforeMiddlewares: [validateSsoProviderId, validateSsoCallbackUrls, authorizeSsoRegistration] as const,
 
 	isSsoCallback: isSsoCallbackRequest,
 
diff --git a/app/server/modules/sso/sso.service.ts b/app/server/modules/sso/sso.service.ts
index d2359bc6..996041fd 100644
--- a/app/server/modules/sso/sso.service.ts
+++ b/app/server/modules/sso/sso.service.ts
@@ -1,6 +1,6 @@
 import { db } from "~/server/db/db";
-import { ssoProvider, account, invitation, organization } from "~/server/db/schema";
-import { eq, and } from "drizzle-orm";
+import { ssoProvider, account, invitation, organization, sessionsTable } from "~/server/db/schema";
+import { eq, and, inArray } from "drizzle-orm";
 import { isReservedSsoProviderId } from "./utils/sso-provider-id";
 import { normalizeEmail } from "./utils/sso-context";
 
@@ -83,9 +83,19 @@ export class SsoService {
 				return true;
 			}
 
+			const affectedAccounts = await tx.query.account.findMany({
+				where: { providerId: provider.providerId },
+				columns: { userId: true },
+			});
+			const affectedUserIds = [...new Set(affectedAccounts.map((row) => row.userId))];
+
 			await tx.delete(account).where(eq(account.providerId, provider.providerId));
 			await tx.delete(ssoProvider).where(eq(ssoProvider.id, provider.id));
 
+			if (affectedUserIds.length > 0) {
+				await tx.delete(sessionsTable).where(inArray(sessionsTable.userId, affectedUserIds));
+			}
+
 			return true;
 		});
 	}
diff --git a/app/server/utils/restic/helpers/__tests__/validate-custom-params.test.ts b/app/server/utils/restic/helpers/__tests__/validate-custom-params.test.ts
new file mode 100644
index 00000000..1599f07b
--- /dev/null
+++ b/app/server/utils/restic/helpers/__tests__/validate-custom-params.test.ts
@@ -0,0 +1,44 @@
+import { describe, expect, test } from "bun:test";
+import { validateCustomResticParams } from "../validate-custom-params";
+
+describe("validateCustomResticParams", () => {
+	test("accepts supported flags and values", () => {
+		const result = validateCustomResticParams([
+			"--no-scan",
+			"--read-concurrency 8",
+			"--exclude-larger-than 500M",
+			"--pack-size=64",
+		]);
+
+		expect(result).toBeNull();
+	});
+
+	test("rejects positional arguments", () => {
+		const result = validateCustomResticParams(["/etc"]);
+
+		expect(result).toContain('Unexpected positional argument "/etc"');
+	});
+
+	test("rejects extra positional arguments after a flag value", () => {
+		const result = validateCustomResticParams(["--read-concurrency 8 /etc"]);
+
+		expect(result).toContain('Unexpected positional argument "/etc"');
+	});
+
+	test("rejects unsupported path-bearing flags", () => {
+		const result = validateCustomResticParams(["--cache-dir /tmp/restic-cache"]);
+
+		expect(result).toContain('Unknown or unsupported flag "--cache-dir"');
+	});
+
+	test("rejects dry-run flags", () => {
+		expect(validateCustomResticParams(["--dry-run"])).toContain('Unknown or unsupported flag "--dry-run"');
+		expect(validateCustomResticParams(["-n"])).toContain('Unknown or unsupported flag "-n"');
+	});
+
+	test("rejects missing values for flags that require one", () => {
+		const result = validateCustomResticParams(["--read-concurrency"]);
+
+		expect(result).toBe('Flag "--read-concurrency" requires a value');
+	});
+});
diff --git a/app/server/utils/restic/helpers/validate-custom-params.ts b/app/server/utils/restic/helpers/validate-custom-params.ts
index 07e945d8..e17aec76 100644
--- a/app/server/utils/restic/helpers/validate-custom-params.ts
+++ b/app/server/utils/restic/helpers/validate-custom-params.ts
@@ -14,56 +14,106 @@ const DENIED_FLAGS = new Set<string>([
 	"--repo",
 ]);
 
-const ALLOWED_FLAGS = new Set<string>([
-	"--verbose",
-	"-v",
-	"--no-scan",
-	"--exclude-larger-than",
-	"--skip-if-unchanged",
-	"--exclude-caches",
-	"--force",
-	"--use-fs-snapshot",
-	"--read-concurrency",
-	"--ignore-ctime",
-	"--ignore-inode",
-	"--with-atime",
-	"--no-cache",
-	"--cleanup-cache",
-	"--cache-dir",
-	"--limit-upload",
-	"--limit-download",
-	"--pack-size",
-	"--dry-run",
-	"-n",
-	"--no-lock",
-	"--json",
+type FlagSpec = {
+	requiresValue: boolean;
+	validateValue?: (value: string) => string | null;
+};
+
+const positiveIntegerValue = (value: string) => {
+	return /^\d+$/.test(value) ? null : `Flag value "${value}" must be a positive integer`;
+};
+
+const FLAG_SPECS = new Map<string, FlagSpec>([
+	["--verbose", { requiresValue: false }],
+	["-v", { requiresValue: false }],
+	["--no-scan", { requiresValue: false }],
+	["--exclude-larger-than", { requiresValue: true }],
+	["--skip-if-unchanged", { requiresValue: false }],
+	["--exclude-caches", { requiresValue: false }],
+	["--force", { requiresValue: false }],
+	["--use-fs-snapshot", { requiresValue: false }],
+	["--read-concurrency", { requiresValue: true, validateValue: positiveIntegerValue }],
+	["--ignore-ctime", { requiresValue: false }],
+	["--ignore-inode", { requiresValue: false }],
+	["--with-atime", { requiresValue: false }],
+	["--no-cache", { requiresValue: false }],
+	["--cleanup-cache", { requiresValue: false }],
+	["--limit-upload", { requiresValue: true, validateValue: positiveIntegerValue }],
+	["--limit-download", { requiresValue: true, validateValue: positiveIntegerValue }],
+	["--pack-size", { requiresValue: true, validateValue: positiveIntegerValue }],
+	["--no-lock", { requiresValue: false }],
 ]);
 
-function extractFlagName(token: string): string | null {
-	if (!token.startsWith("-")) {
-		return null;
-	}
+const ALLOWED_FLAGS = [...FLAG_SPECS.keys()].join(", ");
+
+function parseFlagToken(token: string) {
 	const eqIdx = token.indexOf("=");
-	return eqIdx === -1 ? token : token.slice(0, eqIdx);
+
+	return eqIdx === -1
+		? { flag: token, inlineValue: null as string | null }
+		: { flag: token.slice(0, eqIdx), inlineValue: token.slice(eqIdx + 1) };
+}
+
+function validateFlagValue(flag: string, value: string, spec: FlagSpec): string | null {
+	if (!value) {
+		return `Flag "${flag}" requires a value`;
+	}
+
+	if (value.startsWith("-")) {
+		return `Flag "${flag}" requires a value, but received "${value}"`;
+	}
+
+	return spec.validateValue?.(value) ?? null;
 }
 
 export function validateCustomResticParams(params: string[]): string | null {
 	for (const param of params) {
 		const tokens = param.trim().split(/\s+/).filter(Boolean);
 
-		for (const token of tokens) {
-			const flag = extractFlagName(token);
-			if (flag === null) {
-				continue;
+		for (let index = 0; index < tokens.length; index += 1) {
+			const token = tokens[index];
+
+			if (!token.startsWith("-")) {
+				return `Unexpected positional argument "${token}" in customResticParams`;
 			}
 
+			const { flag, inlineValue } = parseFlagToken(token);
+
 			if (DENIED_FLAGS.has(flag)) {
 				return `Flag "${flag}" is not permitted in customResticParams`;
 			}
 
-			if (!ALLOWED_FLAGS.has(flag)) {
-				return `Unknown or unsupported flag "${flag}" in customResticParams. Permitted flags: ${[...ALLOWED_FLAGS].join(", ")}`;
+			const spec = FLAG_SPECS.get(flag);
+			if (!spec) {
+				return `Unknown or unsupported flag "${flag}" in customResticParams. Permitted flags: ${ALLOWED_FLAGS}`;
 			}
+
+			if (!spec.requiresValue) {
+				if (inlineValue !== null && inlineValue !== "") {
+					return `Flag "${flag}" does not accept a value`;
+				}
+				continue;
+			}
+
+			if (inlineValue !== null) {
+				const error = validateFlagValue(flag, inlineValue, spec);
+				if (error) {
+					return error;
+				}
+				continue;
+			}
+
+			const nextToken = tokens[index + 1];
+			if (!nextToken) {
+				return `Flag "${flag}" requires a value`;
+			}
+
+			const error = validateFlagValue(flag, nextToken, spec);
+			if (error) {
+				return error;
+			}
+
+			index += 1;
 		}
 	}